The present invention relates to a digital remote control method in which data bits "0" and "1" are identified according to different pulse intervals, and the pulses are transmitted after being modulated with a signal of a particular frequency. More particularly, the invention relates to a digital remote control device which includes a custom code and which is obtained by improving a data code forming a transmission instruction.
An example of a conventional ordinary remote control system will be described with reference to FIG. 1. In FIG. 1, reference numeral 1 designates a signal transmitting circuit; 2, a signal receiving circuit; 3, a light-emitting section composed of light-emitting diodes or other light-emitting elements which generate light in response to the output of the signal transmitting circuit 1; and 4, a light-detecting section composed of photodiodes or other light-detecting elements which receive a light signal 5 from the light-emitting section 3. The output of the light-detecting section 4 is applied to the signal receiving circuit 2.
In the remote control system thus constructed, data to be transmitted is encoded and modulated by the signal transmitting circuit 1, and the output of the signal transmitting circuit 1 is converted into the light signal 5 by the light-emitting section 3, which signal 5 is transmitted. The light signal 5 thus transmitted is received by the light-detecting section 4 and demodulated by the signal receiving circuit 2.
In the transmission system of the device of this type, the data bits "0" and "1" are distinguished by different pulse intervals, as shown in FIGS. 2A and 2B which indicate pulse waveforms representing bits "0" and "1". That is, "0" is represented by a short pulse interval 11 as shown in FIG. 2A and "1" is represented by a long pulse interval 12 as shown in FIG. 2B.
Heretofore a data coding method has been employed in which, as shown in FIG. 3 indicating a conventional transmission code format, several bits "0" and "1" are combined into one word 21, and instructions are classified according to the data code represented by the word 21. In addition, in order to avoid interference with other remote control systems, some bits of the transmission code are assigned to a custom code (such as may be indicative of the transmitting system) while the remaining bits are assigned to an instruction code. For instance when, of 10 bits forming a transmission code, 3 bits are employed as a custom code and 7 bits are employed as an instruction code, 8 (=2.sup.3) kinds of independent systems each having 128 (=2.sup.7) instructions can be formed. In FIG. 3, reference numeral 22 designates the repetitive period of the transmission code.
In more detail, as shown in FIG. 4, on the signal transmitting side, when a key in a key-matrix 10 is depressed, a key input read circuit 11 detects the key thus depressed and applies data representative thereof to a code modulation circuit 12, control signals for which are supplied by a timing generator 13 receiving timing pulses from a clock oscillator 14. In the code modulation circuit 12, a data code corresponding to this data is produced and converted into pulse intervals representing "0" and "1". The output of the code modulation circuit 12 is applied to a transistor of a driver circuit 15, thereby to drive a light-emitting diode 16 to cause the latter to output a light signal.
On the signal receiving side, the transmitted light signal is received by a photodiode 17, the output of which is applied through a preamplifier to a remote control signal demodulation circuit 19. The signal thus applied is demodulated and outputted.
A variety of remote control systems of different bit arrangements have been proposed in the art. However, since they are similar to one another in "0" and "1" decision reference and in bit number, they all suffer from signal interference; that is, they cannot be used for remote control purposes.